Chunqin Zou

Iron and Zinc Concentrations in Grain and Flour of Winter Wheat As Affected by Foliar Application

Human deficiencies of iron (Fe) and zinc (Zn) are worldwide problems. Biofortification of wheat could reduce Fe and Zn deficiencies in societies that depend on wheat consumption. This study investigated the effects of foliar application of Fe with or without Zn on the concentrations of Fe and Zn in grain and especially in flour of three wheat cultivars. On average, grain Fe concentration was increased significantly from 29.5 mg kg(-1) in the control to 37.8, 35.9, or 34.9 mg kg(-1) by application of FeSO4, ferric citrate plus ZnSO4, or ferric citrate, respectively. As expected, grain Zn concentration was increased from 29.0 mg kg(-1) in the control to 45.7 or 39.6 mg kg(-1) by application of ferric citrate plus ZnSO4 or a complex of micronutrients. Although the Fe and Zn concentrations in flour were inherently lower than in bran and shorts made by experimental mill, the concentrations in flour were simultaneously increased from 10.4 to 12.4 mg kg(-1) for Fe and from 11.8 to 17.4 mg kg(-1) for Zn by application of ferric citrate plus ZnSO4. Importantly, Fe was peripherally localized within grain fractions and strictly limited to transport to endosperm, making it more difficult to increase the quantity of Fe in flour products by foliar Fe application, but the situation with Zn is promising because Zn is more readily transported to the endosperm than Fe. The current study increases the understanding of agronomic biofortification.

Mycorrhizal responsiveness of aerobic rice genotypes is negatively correlated with their zinc uptake when nonmycorrhizal

Plant Zn uptake from low Zn soils can be increased by Zn-mobilizing chemical rhizosphere processes. We studied whether inoculation with arbuscular mycorrhizal fungi (AMF) can be an additional or an alternative strategy. We determined the effect of AMF inoculation on growth performance and Zn uptake by rice genotypes varying in Zn uptake when nonmycorrhizal. A pot experiment was conducted with six aerobic rice genotypes inoculated with Glomus mosseae or G. etunicatum or without AMF on a low Zn soil. Plant growth, Zn uptake and mycorrhizal responsiveness were determined. AMF-inoculated plants produced more biomass and took up more Zn than nonmycorrhizal controls. Mycorrhizal inoculation, however, significantly increased Zn uptake only in genotypes that had a low Zn uptake in the nonmycorrhizal condition. We conclude that genotypes that are less efficient in Zn uptake when nonmycorrhizal are more responsive to AMF inoculation. We provide examples from literature allowing generalization of this conclusion on a trade off between mycorrhizal responsiveness and nutrient uptake efficiency.

FROM FLOODED TO AEROBIC CONDITIONS IN RICE CULTIVATION: CONSEQUENCES FOR ZINC UPTAKE

Scarcity of water causes a shift from flooded to aerobic conditions for rice production in zinc deficient areas in Northern China. This shift alters soil conditions that affect zinc availability to the crop. This paper concerns the effect of aerobic compared to flooded conditions on crop biomass production, grain yield and zinc content. A field experiment was done with six rice genotypes (Oryza sativa L.) grown on a calcareous soil, both with (23 kg Zn ha−1) and without Zn fertilization. Sampling was conducted at tillering and physiological mature stage. Zn concentration in the shoots was significantly lower at both stages in plants grown in the aerobic field. At maturity, Zn uptake, biomass production, grain yield and Zn-harvest index [grain Zn/(shoot + grain Zn)] were lower under aerobic cultivation. Rice genotypes including aerobic rice and lowland rice differ in degree of response to low Zn supply. A twofold difference was found among aerobic genotypes in grain yield and Zn uptake. Also Zn-harvest index varied significantly. Zn application affected neither grain yield nor grain Zn content, although it significantly improved biomass production in both systems in most genotypes. These results demonstrate that introduction of aerobic rice systems on calcareous soils may increase Zn deficiency problems.

The reduction in zinc concentration of wheat grain upon increased phosphorus-fertilization and its mitigation by foliar zinc application

Background and aimsMalnutrition resulting from zinc (Zn) and iron (Fe) deficiency has become a global issue. Excessive phosphorus (P) application may aggravate this issue due to the interactions of P and micronutrients in soil crop. Crop grain micronutrients associated with P applications and the increase of grain Zn by Zn fertilization were field-evaluated.MethodsA field experiment with wheat was conducted to quantify the effect of P applications on grain micronutrient quality during two cropping seasons. The effect of foliar Zn applications on grain Zn quality with varied P applications was tested in 2011.ResultsPhosphorus applications decreased grain Zn concentration by 17–56%, while grain levels of Fe, manganese (Mn) and copper (Cu) either remained the same or increased. Although P applications increased grain yield, they restricted the accumulation of shoot Zn, but enhanced the accumulation of shoot Fe, Cu and especially Mn. In 2011, foliar Zn application restored the grain Zn to levels occurring without P and Zn application, and consequently reduced the grain P/Zn molar ratio by 19–53% than that without Zn application.ConclusionsFoliar Zn application may be needed to achieve both favorable yield and grain Zn quality of wheat in production areas where soil P is building up.

Improving zinc bioavailability in transition from flooded to aerobic rice. A review

Zinc (Zn) deficiency is a widely occurring constraint for rice production and for human nutrition. Scarcity of water is leading to a shift from flooded to aerobic rice production, which can have an impact on Zn deficiency in rice. Zinc bioavailability is a function of both soil and plant factors that can be altered by water management, particularly in relation to conditions in the rhizosphere. Biogeochemical modeling based on bulk soil conditions failed to predict the effect of water management on Zn bioavailability, but revealed that dissolved organic anions, pH, and redox conditions were major determinants. Rhizosphere sampling is needed to understand the difference in Zn mobilization and uptake between flooded and aerobic cultivation systems. Zinc bioavailability is not only affected by changes in the chemical properties of the soils, but also by biological processes such as mycorrhizal inoculation and root release of organic compounds into rhizosphere. Phytosiderophores and organic acids are two classes of Zn chelators secreted from roots that have been linked to the release of Zn from soil-bound forms and its subsequent uptake by plants. A shift to aerobic condition provides a favorable environment for activity of mycorrhizal fungi and enhanced mycorrhizal inoculation under aerobic conditions has been shown to increase plant Zn uptake. Aerobic rice genotypes with varying tolerance to Zn deficiency display a trade-off between mycorrhizal Zn responsiveness and root exudation of Zn chelator in the rhizosphere, which is probably due to a competition for carbon. Potential agronomic management practices in aerobic rice production systems are discussed, with an emphasis on their roles in improving bioavailability of Zn. Addition of Zn fertilizers by soil or foliar application have been shown to increase Zn concentration in cereal grains but the extent of the increase differs among crop species. The shift from flooded to aerobic condition can cause significant N transformations, which may consequently affect Zn mobilization and uptake. An appropriate N management strategy, including an effective combination of source, rate, application method, and timing, should consider the effects on soil pH. Application of P fertilizer should be done with careful consideration to the effect on Zn uptake. A reasonable cropping system (intercropping and crop rotation) could prevent Zn deficiency and offer an effective and sustainable pathway to Zn biofortification. Keeping these points in mind, this review describes our current knowledge of Zn bioavailability as affected by changes in soil–plant interactions caused by the transition from flooded to aerobic rice cultivation.

Senescence-induced iron mobilization in source leaves of barley (Hordeum vulgare) plants

• Retranslocation of iron (Fe) from source leaves to sinks requires soluble Fe binding forms. As much of the Fe is protein-bound and associated with the leaf nitrogen (N) status, we investigated the role of N in Fe mobilization and retranslocation under N deficiency- vs dark-induced leaf senescence. • By excluding Fe retranslocation from the apoplastic root pool, Fe concentrations in source and sink leaves from hydroponically grown barley (Hordeum vulgare) plants were determined in parallel with the concentrations of potential Fe chelators and the expression of genes involved in phytosiderophore biosynthesis. • N supply showed opposing effects on Fe pools in source leaves, inhibiting Fe export out of source leaves under N sufficiency but stimulating Fe export from source leaves under N deficiency, which partially alleviated Fe deficiency-induced chlorosis. Both triggers of leaf senescence, shading and N deficiency, enhanced NICOTIANAMINE SYNTHASE2 gene expression, soluble Fe pools in source leaves, and phytosiderophore and citrate rather than nicotianamine concentrations. • These results indicate that Fe mobilization within senescing leaves is independent of a concomitant N sink in young leaves and that phytosiderophores enhance Fe solubility in senescing source leaves, favoring subsequent Fe retranslocation.

Effects of Nitrogen on the Distribution and Chemical Speciation of Iron and Zinc in Pearling Fractions of Wheat Grain

Increasing nitrogen supply can increase Fe and Zn concentrations in wheat grain, but the underlying mechanisms remain unclear. Size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry was used to determine Fe and Zn speciation in the soluble extracts of grain pearling fractions of two wheat cultivars grown at two N rates (100 and 350 kg of N ha(-1)). Increasing N supply increased the concentrations of total Fe and Zn and the portions of Fe and Zn unextractable with a Tris-HCl buffer and decreased the concentrations of Tris-HCl-extractable (soluble) Fe and Zn. Within the soluble fraction, Fe and Zn bound to low molecular weight compounds, likely to be Fe-nicotianamine and Fe-deoxymugineic acid or Zn-nicotianamine, were decreased by 5-12% and 4-37%, respectively, by the high N treatment, whereas Fe and Zn bound to soluble high molecular weight or soluble phytate fractions were less affected. The positive effect of N on grain Fe and Zn concentrations was attributed to an increased sink in the grain, probably in the form of water-insoluble proteins.

Potassium and Nitrogen Distribution Pattern and Growth of Flue-Cured Tobacco Seedlings Influenced by Nitrogen Form and Calcium Carbonate in Hydroponic Culture

ABSTRACT The influences of nitrogen form (NH4 +, NO3 −, and NH4NO3) with or without CaCO3 on the growth and potassium (K) and nitrogen (N) uptake and partitioning of flue-cured tobacco plants (Nicotiana tabacum L. cv. ‘K326’) were examined under the controlled conditions of nutrient-solution culture. Tobacco seedlings with four true leaves were grown in mixed substrate before being transplanted and grown in a pre-culture solution until the six-true-leaf stage. The following treatments were applied: NH4 +-, NO3 −-, and NH4NO3 alone, and each of these in combination with CaCO3. Seventeen days later, the plants were harvested. The results showed that NH4 + as the only N source resulted in lower dry weight of both leaves and roots compared with other N forms, including NO3 − and NH4NO3, without obvious ammonia toxicity in leaves. The CaCO3 addition was beneficial in ameliorating the growth suppression found in NH4 +-only plants, but the same effects of addition were not found in NO3 −-only plants. Sole NH4 + nutrition led to the lowest K concentration and content in leaves and roots, while sole NO3 −-only plants had the highest. Added CaCO3 also significantly improved the K concentration and content in NH4 +-only plants. However, NH4 + nutrition resulted in more K translocated to leaves than did NO3 − supply. Nitrogen concentration and content were only weakly affected by N form. Although NH4 +-only plants had the lowest N concentration and content in plants, there was no difference in N concentration in top leaves and roots between NH4 + and NO3 −-plants. Added CaCO3 also improved the N concentration in NH4 +-only plants. In contrast to its effect on K partitioning, the NH4 +-only treatment the lowest N concentration in leaves, while no differences in N partitioning were observed under other treatments. These results suggest that long-term use of 100% NH4 + in the nutrient solution reduces dry-matter accumulation and K uptake in tobacco plants and increases K accumulation in leaves. Added CaCO3 could reduced the suppression induced by 100% NH4 + to a certain extent.

Zinc, iron, manganese and copper uptake requirement in response to nitrogen supply and the increased grain yield of summer maize.

The relationships between grain yields and whole-plant accumulation of micronutrients such as zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) in maize (Zea mays L.) were investigated by studying their reciprocal internal efficiencies (RIEs, g of micronutrient requirement in plant dry matter per Mg of grain). Field experiments were conducted from 2008 to 2011 in North China to evaluate RIEs and shoot micronutrient accumulation dynamics during different growth stages under different yield and nitrogen (N) levels. Fe, Mn and Cu RIEs (average 64.4, 18.1and 5.3 g, respectively) were less affected by the yield and N levels. ZnRIE increased by 15% with an increased N supply but decreased from 36.3 to 18.0 g with increasing yield. The effect of cultivars on ZnRIE was similar to that of yield ranges. The substantial decrease in ZnRIE may be attributed to an increased Zn harvest index (from 41% to 60%) and decreased Zn concentrations in straw (a 56% decrease) and grain (decreased from 16.9 to 12.2 mg kg−1) rather than greater shoot Zn accumulation. Shoot Fe, Mn and Cu accumulation at maturity tended to increase but the proportions of pre-silking shoot Fe, Cu and Zn accumulation consistently decreased (from 95% to 59%, 90% to 71% and 91% to 66%, respectively). The decrease indicated the high reproductive-stage demands for Fe, Zn and Cu with the increasing yields. Optimized N supply achieved the highest yield and tended to increase grain concentrations of micronutrients compared to no or lower N supply. Excessive N supply did not result in any increases in yield or micronutrient nutrition for shoot or grain. These results indicate that optimized N management may be an economical method of improving micronutrient concentrations in maize grain with higher grain yield.

Harvesting more grain zinc of wheat for human health

Increasing grain zinc (Zn) concentration of cereals for minimizing Zn malnutrition in two billion people represents an important global humanitarian challenge. Grain Zn in field-grown wheat at the global scale ranges from 20.4 to 30.5 mg kg−1, showing a solid gap to the biofortification target for human health (40 mg kg−1). Through a group of field experiments, we found that the low grain Zn was not closely linked to historical replacements of varieties during the Green Revolution, but greatly aggravated by phosphorus (P) overuse or insufficient nitrogen (N) application. We also conducted a total of 320-pair plots field experiments and found an average increase of 10.5 mg kg−1 by foliar Zn application. We conclude that an integrated strategy, including not only Zn-responsive genotypes, but of a similar importance, Zn application and field N and P management, are required to harvest more grain Zn and meanwhile ensure better yield in wheat-dominant areas.